Inhibition of Notch signalling has ability to alter the proximal and distal TCR signalling events in human CD3+ αβ T-cells

The Notch signalling pathway is an important regulator of T cell function and is known to regulate the effector functions of T cells driven by T cell receptor (TCR). However, the mechanism integrating these pathways in human CD3(+) alpha beta T cells is not well understood. The present study was carried out to investigate how Notch and TCR driven signalling are synchronized in human all T cells. Differential expression of Notch receptors, ligands, and target genes is observed on human alpha beta T cells which are upregulated on stimulation with alpha-CD3/CD28 mAb. Inhibition of Notch signalling by GSI-X inhibited the activation of T cells and affected proximal T cell signalling by regulating CD3-zeta; chain expression. Inhibition of Notch signalling decreased the protein expression of CD3-zeta chain and induced expression of E3 ubiquitin ligase (GRAIL) in human all T cells. Apart from affecting proximal TCR signalling, Notch signalling also regulated the distal TCR signalling events. In the absence of Notch signalling, alpha-CD3/CD28 mAb induced activation and IFN-gamma production by alpha beta T cells was down-modulated. The absence of Notch signalling in human alpha beta T cells inhibited proliferative responses despite strong signalling through TCR and IL-2 receptor. This study shows how Notch signalling cooperates with TCR signalling by regulating CD3-zeta chain expression to support proliferation and activation of human alpha beta T cells.